Floods

Floods are the most frequent type of natural disaster and occur when an overflow of water submerges land that is usually dry. Floods are often caused by heavy rainfall, rapid snowmelt or a storm surge from a tropical cyclone or tsunami in coastal areas.

Floods can cause widespread devastation, resulting in loss of life and damages to personal property and critical public health infrastructure. Between 1998-2017, floods affected more than 2 billion people worldwide. People who live in floodplains or non-resistant buildings, or lack warning systems and awareness of flooding hazard, are most vulnerable to floods.

There are 3 common types of floods:

• Flash floods are caused by rapid and excessive rainfall that raises water heights quickly, and rivers, streams, channels or roads may be overtaken.
• River floods are caused when consistent rain or snow melt forces a river to exceed capacity. 
• Coastal floods are caused by storm surges associated with tropical cyclones and tsunami.

Between 80-90% of all documented disasters from natural hazards during the past 10 years have resulted from floods, droughts, tropical cyclones, heat waves and severe storms. Floods are also increasing in frequency and intensity, and the frequency and intensity of extreme precipitation is expected to continue to increase due to climate change.

Drowning accounts for 75% of deaths in flood disasters. Flood disasters are becoming more frequent and this trend is expected to continue. Drowning risks increase with floods particularly in low- and middle-income countries where people live in flood prone areas and the ability to warn, evacuate, or protect communities from floods is weak or only just developing. 

Deaths also result from physical trauma, heart attacks, electrocution, carbon monoxide poisoning or fire associated with flooding. Often, only immediate traumatic deaths from flooding are recorded. 

Floods can also have medium- and long-term health impacts, including:

• water- and vector-borne diseases, such as cholera, typhoid or malaria
• injuries, such as lacerations or punctures from evacuations and disaster cleanup 
• chemical hazards
• mental health effects associated with emergency situations
• disrupted health systems, facilities and services, leaving communities without access to health care 
• damaged basic infrastructure, such as food and water supplies, and safe shelter.

The magnitude of the physical and human costs from floods can be reduced if adequate emergency prevention, preparedness, response and recovery measures are implemented in a sustainable and timely manner. 

WHO works with Member States to build resilient and proactive health systems that can anticipate the needs and challenges during emergencies so that they are more likely to reduce risks and respond effectively when needed.

As the health cluster lead for global emergencies, WHO works with partners to respond to:

• ensure appropriate food supplementation 
• restore primary care services, like immunization, child and maternal health, and mental health
• assemble mobile health teams and outreach
• conduct epidemic surveillance, early warning and response
• call for emergency funding to support health action.